Security systems are becoming increasingly prevalent for both public buildings and private dwellings. A conventional security system typically uses contact sensors that are monitored and/or controlled by a central panel that is usually mounted in the house. Various sensors can be installed at windows, doors, and other locations to detect intrusion, e.g. one sensor per door or window. A typical house (e.g. with a size of 1500 sqft) may need at least 6-8 sensors. This induces a considerable hardware cost. The installation of the conventional security system (especially the wiring) is tedious, time consuming and expensive. A conventional security system is very difficult, if not impossible, to upgrade, which is needed over time as technology develops. Maintenance and repair of a conventional security system are also tedious, expensive, and close to impossible.
In addition, existing security systems based on object motion detection cannot provide enough accuracy and often lead to false alarms. Existing approaches include those based on passive infrared (PIR), active infrared (AIR) and Ultrasonic. PIR sensors are the most widely used motion sensor in home security systems, and can detect human motions by sensing the difference between background heat and the heat emitted by moving people. However, systems based on PIR sensors are prone to false alarms due to its sensitivity to environmental changes, like hot/cold air flow and sunlight. They are easily defeated by blocking the body heat emission by e.g. wearing a heat-insulating full-body suit. Their range is limited and need a line-of-sight (LOS) condition; thus multiple devices are needed. In AIR based systems, an IR emitter sends a beam of IR which will be received by an IR receiver. When the beam is interrupted, a motion is detected. This solution can be easily seen using a regular camera or any IR detection mechanism and also has a limited range and thus needs LOS. Ultrasonic sensors detect human motion by sending out ultrasonic sound waves into a space and measuring the speed at which they return, and motion can be detected if there is a frequency change. But this approach can be defeated by wearing an anechoic suit. Also, ultrasound cannot penetrate solid objects such as furniture or boxes, which causes gaps in detection field. Slow movements by a burglar may not trigger an alarm in this case.
Therefore, there is a need for apparatus and methods for recognizing events (e.g. events related to object motion and/or security) to solve the above-mentioned problems and to avoid the above-mentioned drawbacks.